Instead Mozilla has made the curious decision to pull the plug on the long-delayed project, while offering only small clues as to why the decision was made.

The announcement was posted by Mozilla Engineering Manager Benjamin Smedberg on the Bugzilla development page. He ordered Mozilla employees and community developers:

Please stop building windows 64 builds and tests.

As for why the he opted to pull the plug on 64-bit for now, he comments, "Many plugins are not available in 64-bit versions. The plugins that are available don’t work correctly in Firefox because we haven’t implemented things like windowproc hooking, which means that hangs are more common."

Firefox 64-bit development is dead for now. [Image Source: Flickr/dimnikolov]

There's even a 64-bit version of IE bundled with WinXP x64. It actually worked quite well considering how long ago that was. The reason it wasn't set as default in those days had to do with compatibility with "extras". Flash and Java support for one, and it didn't support 32-bit add-ins, activex controls. Flash and Java both dragged their feet on proper 64-bit support. Nowadays I don't think that's much of an issue, though.

That mostly applied to IE9 IIRC. With IE8 I believe they both used the same javascript engines. IE9 introduced Chakra only on 32-bit. I guess they didn't want to delay it any further, and most users still didn't run the 64-bit version.

However, with IE10 you shouldn't see a repeat of this scenario. Both 32-bit and 64-bit IE10 should be about the same, the 64-bit version might even be a hair better. Also they said that IE10 Metro (since it doesn't run add-ons anyway and uses internal engines only for stuff) defaults to 64-bit. That's good for tablets especially. Desktop IE10 still defaults to 32-bit for compatiblity with add-ons, etc. So there's no loss of function there.